Photo by John Burns

MEASURE OF SEVERITY

Severity is the quantity of disease affecting the sampling unit. For corals, severity is the quantity of disease affecting an individual coral colony or a group of surveyed colonies. Severity measures are typically expressed as a proportion or percentage of the sampling unit that is affected by a disease or reduced health state. For example, if 3/4 of a colony surface area is affected by a certain disease then the severity would be expressed as 75%. 

Severity gives a more accurate measure of the extent to which a disease impacts an affected population since is takes relative cover into account, rather than simple presence or absence of a condition.